The present invention relates to an injection method of a die casting machine for injecting a molten metal into a die cavity.
Die casting machines are classified into those of a vertical casting type and those of a horizontal casting type in accordance with the injection direction of a molten metal into a die cavity. An injection device of a die casting machine of a vertical casting type has a stationary sleeve, split into two semicylinders and fitted under a die cavity, for opening/closing together with a die, an injection sleeve detachably connected to the lower end of the clamped stationary sleeve, and an injection cylinder, which has an injection plunger fitted in the injection sleeve to be vertically movable by a hydraulic pressure, and which stands upright, is inclined, or horizontally moves in the upright state together with the injection sleeve. According to a conventional casting method using such an injection device, a plurality of billets are melted in a melting furnace. A molten metal in a holding furnace is cast into an injection sleeve, separated from a stationary sleeve and inclined together with an injection cylinder, by an automatic casting unit or a manual ladle. Upon casting, the injection sleeve is moved together with the injection cylinder and is connected to the stationary sleeve. Then, the injection plunger is moved upward by a hydraulic pressure, so that the molten metal in the injection sleeve is injected into the die cavity through the stationary sleeve.
With the conventional injection method, however, a large melting furnace, a holding furnace, an automatic casting unit and so on are required. Therefore, installation and maintenance costs are high, a large space is required, and energy loss is large since it is difficult to set the injection amount of the molten metal constant in each injection.
When a plurality of billets are melted, a large quantity of gas is generated. Also, since a large amount of molten metal is held in air and the molten metal is carried in air from the melting furnace to the holding furnace, impurities such as oxides form on the surface of the molten metal, and impurities are mixed in from the ambient environment. The molten metal casting amounts in the injection step vary, and a gas inclusion occurs. These problems degrade the productivity and quality of the products.